The prior art processes with which I am aware for replacing halogen or amine groups attached to silicon by organocarboxylate groups involve a reaction between a carboxylic acid and a halosilane and use amines to scavenge the HCl liberated. By way of example, trichlorosilane and acetic acid diluted in benzene give a yield of approximately 40 percent of theoretical. The same is true using toluene and other prior art solvents with which I am aware. As part of these processes, therefore, it is necessary to distill or otherwise remove the reactants, scavenging agents, and other impurities that are formed from the desired product. In the prior art processes, an appreciable amount of siloxane is produced during the reaction and during the distillation.
The precursor for many of the organosilicon carboxylates presently produced are halogenated silanes and usually chlorinated silanes. Organo groups can be coupled to the silicon atoms by the reaction of silane hydrogen with an olefinic double bond. The product is usually purified by distillation and thereafter the halogens that are attached to the silicon are replaced by organocarboxylate groups such as alkylcarboxyl or arylcarboxyl groups in a second stage reaction. Because of the poor yield that is obtained during the alkylcarboxyl or arylcarboxyl formation, another distillation step is required before substitutions can be made on organo groups attached to the silicon atoms. Because the organocarboxyl substitutions of the prior art give numerous impurities and because of the elevated temperature used in the distillation step, a considerable amount of siloxane is formed and this further decreases the yield. By the time that the prior art has carried out all of the reaction and distillations above referred to, the yield of the product produced is at best a very small percentage of theoretical.
The principal object of the present invention is the provision of a new and improved process for replacing halogens or amine groups attached to a silicon atom by carboxyl groups without using scavenging agents, and in a manner giving better yields than have been possible with prior art processes.
Further objects and advantages will become apparent to those skilled in the art from the following description of the preferred embodiments.